The present invention relates to an apparatus and method for applying ceramic stucco particulates to a ceramic slurry coated fugitive pattern used in manufacture of investment casting ceramic shell molds for casting metals and alloys.
In casting superalloy gas turbine engine blades and vanes using conventional equiaxed and directional solidification techniques, ceramic shell molds with or without a ceramic core therein are filled with molten metal or alloy that is solidified in the mold. The ceramic shell mold is made by the well known lost-wax process where a fugitive (e.g. wax) pattern of the blade, vane or other article to be cast is repeatedly dipped in a ceramic slurry, drained of excess slurry and covered (stuccoed) with a layer of relatively coarse ceramic particulates, such as ceramic sand or stucco, to build up the shell mold wall to a desired wall thickness. The pattern then is selectively removed from the shell mold by thermal or chemical dewaxing techniques, and the green mold is fired to develop adequate mold strength for casting. U.S. Pat. Nos. 5,335,717 and 5,975,188 describe a typical lost wax process sequence to make ceramic investment casting shell molds.
The ceramic stucco particulates are applied to the wet ceramic slurry on the pattern by positioning the slurry coated pattern in an internal chamber of a so-called stucco tower. The stucco tower includes a ceramic stucco hopper at the top of the internal chamber for gravity discharging loose, dry ceramic stucco particulates from the hopper downwardly onto the slurry coated pattern positioned in the chamber through a front access opening thereof. As the ceramic stucco particulates fall by gravity, they push air downwardly in the chamber, creating vortices, turbulence and non-uniform air flow patterns in the chamber and out of the access opening, expelling fine ceramic stucco particulates and dust into the ambient atmosphere. As a result of such irregular air flow, stucco towers used in the past have suffered from problems of uneven distribution of stucco particulates within the tower, resulting in uneven shell mold wall thickness as well as discharge of fine stucco particulates and dust out of the access opening of the tower. Dust collectors have been provided on the stucco tower to collect the fine stucco particulates and dust expelled from the access opening.
An object of the present invention is to provide a stucco tower or other apparatus to provide improved distribution of particulates discharged in a chamber.
Another object of the present invention is to provide a stucco tower or other apparatus that reduces emission of particulates and dust therefrom.
An illustrative embodiment of the present invention provides stucco tower apparatus that includes an internal chamber in which a ceramic slurry coated pattern is positioned and one or more air circulating plenums positioned for circulating air from a lower region toward an upper region of the chamber as stucco particulates are discharged from a hopper above the chamber and fall by gravity onto the ceramic slurry coated pattern. The apparatus preferably includes an air curtain at an access opening to the chamber to reduce emission of stucco particles and dust, especially when the stucco particles are initially released from the hopper before air circulation through the chamber and the air circulation plenums is fully established.
A method embodiment of the present invention involves applying stucco particulates onto ceramic slurry coated pattern, wherein the ceramic slurry coated pattern is positioned in a chamber, stucco particulates are discharged downwardly in the chamber onto the ceramic slurry coated pattern and create a downward air flow in the chamber, and air is circulated from a lower region of the chamber to an upper region of the chamber as the stucco particulates are discharged. An air curtain is formed at an access opening to the chamber to reduce emission of stucco particles and dust.
Although the invention will be described in detail and illustrated with respect to stucco tower apparatus for applying ceramic stucco particles onto a ceramic slurry coated pattern, the invention is not so limited and can comprise apparatus of other types and uses for discharging particulates from an upper region to a lower region in a chamber.
The above objects and advantages of the present invention will become more readily apparent from the following detailed description taken with the following drawings.